1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a wired circuit board suitably used for a suspension board with circuit.
2. Description of the Prior Art
The wired circuit boards used for electronic/electric equipment are usually provided with terminal portions to connect with external connecting terminals.
In recent years, the so-called “flying lead” in which the terminal portions are formed on both sides of the conductive pattern, rather than in only either side thereof, is in widespread use in order to meet the demand for electronic/electric equipment to have increasingly higher density and reduced size. It is known, for example, in a suspension board with circuit used for a hard disk drive that the terminals are provided in the form of flying lead.
To be more specific, the suspension board with circuit comprises a supporting board 1 of stainless steel foil, a base layer 2 of an insulating material formed on the supporting board 1, a conductive pattern 3 formed on the base layer 2 in the form of a specified circuit pattern, and a cover layer 4 of an insulating material, for covering the conductive pattern 3, as shown in FIG. 21. The terminal portions 5 provided in the form of the flying lead are formed on both sides of the conductive pattern 3 in the following manner. The cover layer 4 is opened to expose a front side of the conductive pattern 3, while also the supporting board 1 and the base layer 2 are opened to expose a back side of the conductive pattern 3. If necessary, metal plated layers 6 are formed on the both sides of the thus exposed conductive pattern 3 by nickel/gold plating and the like.
Thereafter, these terminal portions formed as the flying lead are bonded to external connecting terminals by applying supersonic vibration thereto by use of a bonding tool and the like.
In this terminal portion formed as the flying lead, since the both sides of the conductive pattern are exposed, the supersonic vibration is easily transmitted to the terminals. This is suitable for the bonding using the supersonic vibration: on the other hand, this provides the disadvantage that the conductive pattern exposed at both sides thereof is weak in physical strength and is subject to stress concentration at edge portions of the openings in the base layer and cover layer, to cause easy disconnection of the conductive pattern.